In present telephone communications systems, digital communication can be implemented on a T1 or E1 telephone line and can be processed in accordance with primary rate ISDN (PRI) protocol. Under PRI processing, digital data is transmitted serially on a T1 line in twenty-four serial channels (or on an E1 line in thirty-two channels). In T1 communication, twenty-three of the channels are data channels and the twenty-fourth channel is a control channel used for call set-up and maintenance. In E1, thirty data channels and two control channels are used. Data for each of the channels is time multiplexed over the T1/E1 line and is transmitted over the line in serial data packets, with a data packet for each channel being transmitted periodically every twenty-four/thirty-two packets.
The individual data packets are processed in accordance with the type of communication originating on the corresponding channel. For example, data for a telephone call to or from an analog modem can be converted to analog modem format and then transmitted. Alternatively, a call generated under basic rate ISDN (BRI) can be forwarded to a BRI terminal adapter which will convert the digital data to ISDN format accordingly.
The conversion to/from raw digital T1/E1 data can be performed by the local telephone company's central office before the translated data is sent to the recipient. Alternatively, the raw T1/E1 data can be connected directly to a user. The user can apply the data to a PRI interface which splits the raw data into appropriate channels. The data can then be processed according to the format in which it was originated, e.g., analog (voice), BRI, etc.
Conventionally, regardless of whether the call is analog or digital in origination, each call is processed by a separate device. For example, for BRI calls, each call must be individually routed to a separate BRI terminal adapter. Likewise, for voice calls, each call must be routed to its own individual modem. Hence, in conventional systems, in order to process multiple telephone calls simultaneously, the system must include as many terminal adapters and/or modems as there are channels to be simultaneously processed. In situations where the system is expected to process many telephone calls simultaneously, for example, an Internet service provider, the hardware requirements can be extraordinary.